/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    TreeNode* invertTree(TreeNode* root) {
        if(root==nullptr){return root;}
        return invertnode(root);
    }

    TreeNode* invertnode(TreeNode* node){
        if(node==nullptr){return node;}
        TreeNode* tmp=invertnode(node->left);
        node->left=invertnode(node->right);
        node->right=tmp;
        return node;
    }
};